1. Field of the Invention
This invention relates to a thin film magnetic head and more particularly, it is concerned with a substrate for a thin film magnetic head suitable for high recording density.
2. Description of the Prior Art
Generally, bulk heads composed of finely processed ferrite materials have been employed as a magnetic head for magnetic recording and reading. However, these magnetic heads have reached the limit in respect of the fine processing or machining and the permeability of ferrites to meet the lately rising demands for higher recording density and thin film magnetic heads have thus been developed. Some thin film magnetic heads have been put to practical use as a magnetic disk head for a large-sized computer, but their spread or diffused use has not been realized because of problems on the substrate material and low yield. The thin film magnetic head is generally prepared by sufficiently polishing the surface of a wafer with a suitable size, e.g. 50.times.50 to give a polished surface with a roughness of 50 .ANG. and a smoothness of 1.mu., coating the surface with Al.sub.2 O.sub.3 and SiO.sub.2 of several microns in thickness for the purpose of insulation, forming a predetermined magnetic circuit on the insulation film by sputtering or the like and then cutting a single head out. Therefore, for the mass production of such a thin film magnetic head, it is very important to find a substrate material excellent in machinability such as dimensional precision and surface smoothness in addition to the techniques of forming circuits and forming insulation films.
Up to the present time, ferrites and Al.sub.2 O.sub.3 -TiC ceramics have been examined as a substrate material and in particular, Al.sub.2 O.sub.3 -TiC ceramics have been considered most excellent in magnetic property, mechanical property, smoothening machinability, machining workability and uniformity of structure. However, in practice, these materials do not satisfy all of the machining workability, mechanical property and uniformity of structure, and particularly, they have such a problem that the working yield is lower. That is, ceramic materials having excellent mechanical properties and uniform structures are generally inferior in machinability so that they tend to meet with chipping in the step of slicing.